1. Field of the Invention
This invention relates to and has among its objects the provision of improved methods for shrink-proofing knitted fabrics. Further objects of the invention will be obvious from the following description wherein parts and percentages are by weight unless otherwise specified.
2. Description of the Prior Art
In the production of certain woolen knit clothes--for example, overcoats, men's suits, women's skirts, lamb's wool sweaters, and the like--a good thick cloth is preferred, i.e., one in which the threads are so close together and so intermingled that details of the weave cannot be seen even on close inspection. The method usually adapted for the manufacture of such goods is to weave the cloth with the threads normally spaced, and then to make the weave thicker or "fuller." This operation is referred to normally as fulling or milling and is well-known in the art. In such a process the woolen fibers become progressively entangled by means of agitation. The entanglement draws the fibers together, making the fabric denser and more visually and tactily pleasing. Typically, woolen fabrics are fulled by agitating the fabric in a warm, soapy solution for a period of time. This fulling operation is always carried out prior to shrink-resisting the fabric.
In the prior art as exemplified in U.S. Pat. No. 3,084,019 (Whitfield et al) it is known that wool can be shrinkproofed by a process wherein the wool is serially impregnated with two solutions, one solution containing a diamine dispersed in water; the other, a diisocyanate dispersed in an inert, volatile, essentially water-immiscible solvent. In this way a resinous polyurea is formed in situ on the surface of the wool fibers and the fibers become less susceptible to shrinkage.
In attempting to produce a fulled, shrinkproof fabric in accordance with Whitfield et al. one would proceed by first fulling the material as described above, i.e., by agitating in an aqueous solution. At this stage, the fulled fabric can be dried and then shrinkproofed according to the Whitfield process. Alternatively, the fulled fabric can be treated in the wet state provided the polyamine solution is applied to the fabric prior to the diisocyanate solution. If the diisocyanate solution is applied first, the diisocyanate will react with residual water and thus be rendered ineffective as an agent complimentary to a diamine in polyurea formation.
Although diamine addition followed by diisocyanate addition will result in polyurea formation on the fabric, this order of addition is not suitable for industrial scale operations. The fabric must be dried following exposure to the polyamine solution; otherwise, the diisocyanate solution will become contaminated with polyamine rendering the diisocyanate solution useless for subsequent reactions. In addition, undesirable fouling of equipment occurs because of extraneous polyurea resin formation, i.e., other than on the fabric.
However, drying the fabric after exposure to the diamine is not feasible because the fabric discolors (yellows) and degrades under alkaline conditions at elevated temperatures.
For the above reasons, therefore, the fulled fabric must be dried prior to application of the diisocyanate solution. Additional drying steps are costly with respect to both time and energy.